This application is based on Patent Application No. 11-190578 (1999) filed Jul. 5, 1999 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method, and particularly to an ink jet printing apparatus and an ink jet printing method for performing printing using a processing liquid that makes inks insoluble.
2. Description of the Prior Art
Ink jet printing apparatuses, which have advantages such as their capability of simple printing on various printing mediums, are enjoying more and more applications due to their improved print quality. Ink jet printers are not only used personally but also in offices in order to output various types of information, for example. The ink jet printing apparatuses are what are also used as printout apparatuses in facsimile machines, copy machines, and word processors or the like.
Thus, the ink jet printing apparatuses are further desired to provide a higher image quality. Specifically, it is desirable that printed characters such as black letters have high density and have sharp edges without feathering, that is, bleeding in a form of whiskers. In addition, in printing color images, bleeding is desirably prevented at boundaries between colors.
Some conventional methods, which increase the density (for example, OD: optical density) of black characters and form an image with sharp edges, use ink as a black (Bk) ink, what is called a remaining upper part-type ink, which permeates through a plain paper at a relatively low speed so that a coloring material remain at an upper part (shallower part) of a printing medium.
A problem with the use of such an remaining upper part-type ink of Bk, however, is that due to its insufficient fixing capability (permeability), a relatively long time is required to eject printed paper and obtain a printed product, especially to fix the printed image when solid images which have a particularly high duty are printed.
On the other hand, highly permeable inks have generally been used in order to prevent ink from bleeding at boundaries between colors in color images. In this case, however, when the Bk ink is also highly permeable, it is disadvantageously impossible to increase the density of black characters as described above or other problems may result.
In order to solve this problem, a remaining upper part-type Bk ink of lower permeability is used, while the other color inks are highly permeable. Additionally, the bleeding at the boundaries is prevented by allowing the Bk and color inks to be ejected in accordance with a fixed or more amount of time difference, or for the boundaries, by using a process black obtained through compounding from color inks. In this case, however, printing black characters has insufficient fixing capability. Thus, this method does not enable fast printing, as desired particularly in offices.
In addition, a known means for improving, in particular, the fixing capability provides heaters along a paper feed path to evaporate moisture from the inks in order to promote fixation. This configuration enables faster fixing which contributes to faster printing and reduction of feathering and bleeding at the boundaries.
As is apparent from the above description, it is relatively difficult for the conventional techniques to print high-grade black characters or the like and perform printing without bleeding at the boundaries between colors, with a relatively high speed.
More specifically, a mere change in Bk ink permeability does not allow these problems to be simultaneously solved, particularly because there is a tradeoff relationship between the printed character grade such as the density and the fixing capability. This, in turn, can not provide a sufficient solution to the problem of bleeding at the boundaries.
In particular, the method of allowing the inks to be ejected at different points of time or using the process black as described above has difficulties in realizing fast printing. In addition, the method of using the heaters for fixing is not practical because more thermal energy is required to achieve fast printing.
The assignee of the present application has proposed use of a processing liquid for making color materials in ink insoluble, in order to improve the above-described black character grade or to improve color-developing capability. Such processing liquid is originally used to improve water resistance of printed images, but for example, can be used as follows. The processing liquid is ejected before ejection of the ink so that the processing liquid reacts with the ink ejected after and much color material in the ink remains on a surface of the paper, thereby increasing the density and the color-developing capability and preventing feathering from occurring. Additionally, a proposal has been also made to adjust the permeability of the processing liquid to improve the fixing capability of the printed images.
The use of the processing liquid together with the ink as described above is effective in improving the print grade or the fixing capability, but has not successfully prevented the bleeding at the boundaries between the Bk ink and the color ink.
The object of the present invention is to provide an ink jet printing apparatus and an ink jet printing method that allow printing of black characters with a high speed, high density and little feathering to be realized while ensuring water resistance of a printed image and that allow images to be printed with little bleeding at boundaries between colors.
In a first aspect of the present invention, there is provided an ink jet printing method of performing printing by applying to a printing medium, an ink and a processing liquid for making a coloring material in the ink insoluble, the method comprising the step of:
applying the processing liquid to respective areas of the printing medium to which a black ink containing a black coloring material and a color ink are applied, respectively,
wherein the processing liquids is applied for each of the respective areas so that the respective processing liquids do not come in contact with one another on the printing medium.
In a second aspect of the present invention, there is provided an ink jet printing apparatus for performing printing by applying to a printing medium, an ink and a processing liquid for making a coloring material in the ink insoluble, the apparatus comprising:
means for applying the processing liquid to respective areas of the printing medium to which a black ink containing a black coloring material and a color ink are applied, respectively, the respective areas having a boundary between the areas,
wherein the processing liquids is applied for each of the respective areas so that the respective processing liquids do not come in contact with one another on the printing medium.
With the above configuration, in the case of using the processing liquid together with a black and color inks to print an image, in which an image area printed with the black ink and an image area printed with the color ink are mixed, an application of the inks and the processing liquid is controlled so that the respective processing liquid applied to each of the areas of black and inks will not be connected with each other on the printing medium. Consequently, the respective processing liquid can be present within the boundary between the area of the black ink and the area of the color inks, whereby reactants between the Bk ink and the processing liquid are prevented from flowing out to the area of color inks. As a result of this, reducing the bleeding at the boundaries between the area of black ink and the area of color inks can be realized.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.